A proximity sensor in smartphones is a small device that detects the presence or absence of an object, typically the user's face, in close proximity to the phone. Its primary purpose is to control the behavior of the phone during calls and to conserve power when the phone is not in use.
Most proximity sensors in smartphones use an infrared (IR) light-emitting diode (LED) and a corresponding IR light sensor. Here's how it works:
Emitter (IR LED): The proximity sensor contains an IR LED that emits infrared light, which is not visible to the human eye. This LED is usually placed near the top of the phone, typically next to the front-facing camera or earpiece.
Detector (IR Light Sensor): In close proximity to the IR LED, there is an IR light sensor. This sensor is designed to detect the infrared light reflected back from nearby objects.
Detecting Proximity: When you make or receive a call on your smartphone and hold it to your ear, your face gets close to the phone's screen. At this point, the proximity sensor activates.
IR Light Reflection: The emitted infrared light from the IR LED reflects off your face (or any object in proximity) and is captured by the IR light sensor.
Change in Sensor Reading: The IR light sensor detects the intensity of the reflected infrared light. When your face is close to the phone, the intensity of the reflected light is relatively high. However, when you move the phone away from your face, the intensity of the reflected light decreases.
Triggering Actions: The proximity sensor continuously monitors the reflected light intensity. When the sensor detects a significant decrease in intensity (indicating an object moving away), it triggers specific actions. For instance, during a call, when the proximity sensor detects that you have moved the phone away from your face, it can turn on the display again so you can access the dial pad or end the call.
Power Saving: Additionally, when the proximity sensor detects an object (like your face) in close proximity, it can turn off the phone's display. This feature helps to conserve battery life during calls and prevents accidental touches on the screen while the phone is held against your ear.
In summary, a proximity sensor in smartphones uses infrared light and a sensor to detect nearby objects, primarily during phone calls, and control the screen's behavior to enhance user experience and power efficiency.